The present invention relates to a collar for receiving a shaft for a variable valve lift mechanism in a multiple-cylinder internal combustion engine.
Japanese Laid-Open Patent Publication No. 2001-263015 describes a variable valve actuation mechanism for an internal combustion engine. The variable valve actuation mechanism includes a variable valve lift mechanism, which is arranged for each cylinder to adjust the lift amount of intake and exhaust valves. A support pipe (rocker shaft) extends through the center of the variable valve lift mechanism. A control shaft is arranged in the support pipe. The variable valve lift mechanism is pivoted in a state supported by the support pipe. The lift amount of the valve is adjusted by moving the control shaft in the axial direction.
The support pipes are supported by a plurality of supports arranged on a cylinder head between the variable valve lift mechanisms. The supports position the variable valve lift mechanisms in the axial direction. The valve lift mechanisms are positioned in the axial direction with high accuracy so that the movement of the control shaft adjusts the valve lift amount to be the same in every cylinder.
In an internal combustion engine, the cylinder block, cylinder head, and cam carrier are formed from a light alloy or a light metal, such as aluminum, to reduce weight. However, shafts included in the variable valve actuation mechanism, such as the control shaft, are not formed from a light alloy or a light metal and formed from a steel material, such as cast steel or cast iron, to meet the high strength requirements.
The coefficient of thermal expansion differs greatly between light alloy and steel. Thus, when comparing a state in which the engine is cool and a state in which the engine is warm, the control shaft becomes shorter and changes the interval between the supports located closer to the cylinder head and cam carrier. This produces a difference in the relative positions of the control shaft and the variable valve lift mechanism between cylinders close to the basal end of the control shaft and cylinders close to the distal end of the control shaft. Accordingly, the lift amount differs between cylinders. Such difference causes difficulties for adjusting the combustion state of each cylinder with high accuracy. This may generate vibrations or deteriorate emission and cause an undesirable engine operation state.
The rocker shaft, which supports the variable valve lift mechanism, is arranged at the outer side of the control shaft. When the rocker shaft, which receives the control shaft, has a large diameter, the variable valve lift mechanism that receives the rocker shaft is enlarged. This enlarges and increases the weight of the variable valve actuation mechanism, which would contradict the demand for a smaller and lighter internal combustion engine.